In this work we investigate the Fe3O4 (001) surface/water interface by combining several theoretical approaches, ranging from a hybrid functional method (HSE06) to density-functional tight-binding (DFTB) to molecular mechanics (MM). First, we assess the accuracy of the DFTB method to reproduce correctly HSE06 results on structural details and energetics and available experimental data for the adsorption of isolated water, dimers, trimers, etc. up to a water monolayer. Secondly, we build two possible configurations of a second and a third overlayer and perform molecular dynamics simulations with DFTB, monitoring the water orientation, the H-bond network, and ordered water structures formation. To make our models more realistic, we then build a 12-nm thick water multilayer on top of the Fe3O4 (001) surface slab model, which we investigate through MM molecular dynamics. The water layers structuring, revealed by the analysis of the atomic positions from a long MM-MD run for this large MM model, extends up to about 6-7 Å and nicely compares with that observed for a water trilayer model. However, MM and DFTB MD simulations show some discrepancy due to the poor description of the Fe---OH2 distance in MM that calls for further work in the parametrization of the model. * Corresponding author: cristiana.divalentin@unimib.it
SUPPLEMENTARY MATERIALSee supplementary material for further computational details, tables with comparative analysis, figures of the structures for three and six water molecules adsorbed on the top Fe3O4(001) surface, tables with additional structural information, electron density profile of bulk water on the Fe3O4 (001) surface (against liquid) and comparative linear number density profiles of all the systems under investigation.
In
the confined zone between a bidimensional material and a metal
surface, unexpected effects can take place. In this study, we show
that when a nonregular two-dimensional h-BN layer is grown on a Cu(111)
surface, metal adatoms spontaneously pop up from the bulk to fill
the holes in the structure. We provide ample theoretical support to
our findings based on a large set of dispersion-corrected density
functional theory calculations and on a detailed analysis of the electronic
properties and of the chemical processes at this peculiar interface.
The observation can be rationalized in terms of a high affinity of
Cu adatoms toward N-donor species. Defective h-BN, exposing N-terminated
edges, behaves like a giant multi-N-donor macrocyclic ligand that
can encapsulate metal atoms as a consequence of a huge stabilization
deriving from the Cu–N bond formation. Our conclusions could
apply to other metal surfaces and could even stimulate the idea of
trapping different metal atoms from those of the underlying surface
(e.g., more precious but more active metals) for catalytic purposes.
Surface functionalization is found to prevent the reduction
of
saturation magnetization in magnetite nanoparticles, but the underlying
mechanism is still to be clarified. Through a wide set of hybrid density
functional theory (HSE06) calculations on Fe3O4 nanocubes, we explore the effects of the adsorption of various ligands
(containing hydroxyl, carboxylic, phosphonic, catechol, and silanetriol
groups), commonly used to anchor surfactants during synthesis or other
species during chemical reactions, onto the spin and structural disorder,
which contributes to the lowering of the nanoparticle magnetization.
The spin-canting is simulated through a spin-flip process at octahedral
Fe ions and correlated with the energy separation between O2– 2p and FeOct
3+ 3d states. Only multidentate bridging ligands hamper the spin-canting
process by establishing additional electronic channels between octahedral
Fe ions for an enhanced ferromagnetic superexchange interaction. The
presence of anchoring organic acids also interferes with structural
disorder, by disfavoring surface reconstruction.
Doping magnetite surfaces with transition-metal atoms is a promising strategy to improve the catalytic performance toward the oxygen evolution reaction (OER), which governs the overall efficiency of water electrolysis and hydrogen production. In this work, we investigated the Fe 3 O 4 (001) surface as a support material for single-atom catalysts of the OER. First, we prepared and optimized models of inexpensive and abundant transitionmetal atoms, such as Ti, Co, Ni, and Cu, trapped in various configurations on the Fe 3 O 4 (001) surface. Then, we studied their structural, electronic, and magnetic properties through HSE06 hybrid functional calculations. As a further step, we investigated the performance of these model electrocatalysts toward the OER, considering different possible mechanisms, in comparison with the pristine magnetite surface, on the basis of the computational hydrogen electrode model developed by Nørskov and co-workers. Cobalt-doped systems were found to be the most promising electrocatalytic systems among those considered in this work. Overpotential values (∼0.35 V) were in the range of those experimentally reported for mixed Co/Fe oxide (0.2−0.5 V).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.